On Mittwoch, 30. Juli 2008, Chirag Jog wrote:
quoted text
> * J?rgen Mell <j.mell@t-online.de> [2008-07-30 11:01:32]:
> > On Wednesday, 30. July 2008, Thomas Gleixner wrote:
> > > We are pleased to announce the 2.6.26-rt1 tree, which can be
> > > downloaded from the location:
> >
> > The bad news: It produces continuously lots of bug messages in the
> > error logs (cf. attached dmesg.tgz). The error at rtmutex.c:743 was
> > already present in 2.6.25-rt* when ACPI was enabled. The 'using
> > smp_processor_id ()  in preemptible code' is new here with 2.6.26.
> >
>
> This patch should solve some of the bug messages.
> It does two things:
> 1. Change rt_runtime_lock to be a raw spinlock as the comment above it
> says: it is nested inside the rq lock.
>
> 2. Change mnt_writers to be a per_cpu locked variable.
> This eliminates the need for the codepath to disable preemption and
> then potentially sleep, leading to the BUG messages
>
> Signed-Off-By: Chirag <chirag@linux.vnet.ibm.com>
>
>
>
> Index: linux-2.6.26-rt1/kernel/sched.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
quoted text
> --- linux-2.6.26-rt1.orig/kernel/sched.c	2008-07-30 22:37:19.000000000
> +0530 +++ linux-2.6.26-rt1/kernel/sched.c	2008-07-30 22:37:24.000000000
> +0530 @@ -208,7 +208,7 @@
>
>  struct rt_bandwidth {
>  	/* nests inside the rq lock: */
> -	spinlock_t		rt_runtime_lock;
> +	raw_spinlock_t		rt_runtime_lock;
>  	ktime_t			rt_period;
>  	u64			rt_runtime;
>  	struct hrtimer		rt_period_timer;
> @@ -472,7 +472,7 @@
>  	u64 rt_time;
>  	u64 rt_runtime;
>  	/* Nests inside the rq lock: */
> -	spinlock_t rt_runtime_lock;
> +	raw_spinlock_t rt_runtime_lock;
>
>  #ifdef CONFIG_RT_GROUP_SCHED
>  	unsigned long rt_nr_boosted;
> Index: linux-2.6.26-rt1/fs/namespace.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
quoted text
> --- linux-2.6.26-rt1.orig/fs/namespace.c	2008-07-30 22:39:30.000000000
> +0530 +++ linux-2.6.26-rt1/fs/namespace.c	2008-07-30 22:39:36.000000000
> +0530 @@ -178,13 +178,13 @@
>  	unsigned long count;
>  	struct vfsmount *mnt;
>  } ____cacheline_aligned_in_smp;
> -static DEFINE_PER_CPU(struct mnt_writer, mnt_writers);
> +static DEFINE_PER_CPU_LOCKED(struct mnt_writer, mnt_writers);
>
>  static int __init init_mnt_writers(void)
>  {
>  	int cpu;
>  	for_each_possible_cpu(cpu) {
> -		struct mnt_writer *writer =3D &per_cpu(mnt_writers, cpu);
> +		struct mnt_writer *writer =3D &per_cpu_var_locked(mnt_writers, cpu);
>  		spin_lock_init(&writer->lock);
>  		lockdep_set_class(&writer->lock, &writer->lock_class);
>  		writer->count =3D 0;
> @@ -199,7 +199,7 @@
>  	struct mnt_writer *cpu_writer;
>
>  	for_each_possible_cpu(cpu) {
> -		cpu_writer =3D &per_cpu(mnt_writers, cpu);
> +		cpu_writer =3D &per_cpu_var_locked(mnt_writers, cpu);
>  		spin_unlock(&cpu_writer->lock);
>  	}
>  }
> @@ -251,8 +251,8 @@
>  {
>  	int ret =3D 0;
>  	struct mnt_writer *cpu_writer;
> -
> -	cpu_writer =3D &get_cpu_var(mnt_writers);
> +	int cpu =3D 0;
> +	cpu_writer =3D &get_cpu_var_locked(mnt_writers, &cpu);
>  	spin_lock(&cpu_writer->lock);
>  	if (__mnt_is_readonly(mnt)) {
>  		ret =3D -EROFS;
> @@ -262,7 +262,7 @@
>  	cpu_writer->count++;
>  out:
>  	spin_unlock(&cpu_writer->lock);
> -	put_cpu_var(mnt_writers);
> +	put_cpu_var_locked(mnt_writers, cpu);
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(mnt_want_write);
> @@ -273,7 +273,7 @@
>  	struct mnt_writer *cpu_writer;
>
>  	for_each_possible_cpu(cpu) {
> -		cpu_writer =3D &per_cpu(mnt_writers, cpu);
> +		cpu_writer =3D &per_cpu_var_locked(mnt_writers, cpu);
>  		spin_lock(&cpu_writer->lock);
>  		__clear_mnt_count(cpu_writer);
>  		cpu_writer->mnt =3D NULL;
> @@ -332,8 +332,8 @@
>  {
>  	int must_check_underflow =3D 0;
>  	struct mnt_writer *cpu_writer;
> -
> -	cpu_writer =3D &get_cpu_var(mnt_writers);
> +	int cpu =3D 0;
> +	cpu_writer =3D &get_cpu_var_locked(mnt_writers, &cpu);
>  	spin_lock(&cpu_writer->lock);
>
>  	use_cpu_writer_for_mount(cpu_writer, mnt);
> @@ -360,7 +360,7 @@
>  	 * __mnt_writers can underflow.  Without it,
>  	 * we could theoretically wrap __mnt_writers.
>  	 */
> -	put_cpu_var(mnt_writers);
> +	put_cpu_var_locked(mnt_writers, cpu);
>  }
>  EXPORT_SYMBOL_GPL(mnt_drop_write);
>
> @@ -612,7 +612,7 @@
>  	 * can come in.
>  	 */
>  	for_each_possible_cpu(cpu) {
> -		struct mnt_writer *cpu_writer =3D &per_cpu(mnt_writers, cpu);
> +		struct mnt_writer *cpu_writer =3D &per_cpu_var_locked(mnt_writers,
> cpu); if (cpu_writer->mnt !=3D mnt)
>  			continue;
>  		spin_lock(&cpu_writer->lock);
>
>
> --
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Yes, the number of bug messages is reduced very much by this patch,=20
although both messages are still present in the log (cf. attached dmesg).=20
But with the patch they only occur sporadically after the system has=20
completed start-up and no longer continuously. Thanks a lot!

Bye,
           J=FCrgen